火山喷出物发育土壤的比重及颗粒组成测定

利用比重瓶法对火山喷出物发育土壤的比重进行测定,结果表明:玄武岩质火山喷出物发育土壤的比重大于粗面岩质火山喷出物发育土壤的比重;基于粒径小于1 mm土粒测定的比重,玄武岩质火山喷出物和粗面岩质火山喷出物发育土壤的比重均小于一般土壤的平均比重2.65 g cm~(-3);基于粒径小于0.1 mm土粒测定的比重,除个别玄武岩质火山喷出物发育土壤外也小于2.65 g cm~(-3)。分别取比重值为2.65 g cm~(-3)、粒径小于1 mm土粒的实测比重和粒径小于0.1 mm土粒的实测比重,计算不同粒级土粒的沉降时间,并进行颗粒组成的实验研究表明:取不同比重值测定的土壤颗粒组成含量相差较大而且影响土壤质地定名。由于成土母质的矿物组成决定土壤的比重,且土壤颗粒组成的静水沉降实验是在粒径小于0.1 mm土粒的悬液中进行的,所以,准确测定土壤颗粒组成含量,需要区分成土母质的矿物组成,并测定其小于0.1 mm粒径的土粒比重,重新计算沉降时间。     

Species composition of arbuscular mycorrhizal fungi in two mountain meadows with differing management types and levels of plant biodiversity

Species composition of arbuscular mycorrhizal fungi (AMF) was analysed in two differently managed mountain grasslands in Thuringia (Germany). Arbuscular mycorrhizal fungi were studied in the roots of 18 dominant plant species from a total of 56 (32%). Additionally, spores of AMF were isolated from soil samples. Arbuscular mycorrhizal fungi species composition was analysed based on 96 sequences of the internal transcribed spacer of the nuclear ribosomal DNA, 72 originated from mycorrhizal roots, and 24 originated from AMF spores. Phylogenetic analyses revealed a total of 19 AMF species representing all genera of the Glomeromycota except Scutellospora and Pacispora. Despite a different farming intensity, resulting in remarkable differences concerning their plant species diversity (27 against 43 plant species), the diversity of AMF was found to be similar with 11 species on the intensively farmed meadow and ten species on the extensively farmed one. Nevertheless, species composition between both sites was clearly different. It thus seems likely that the AMF species composition, but not necessarily the species number, is related to above ground plant biodiversity in the system under study.     

Soil fumigation and compost amendment alter soil microbial community composition but do not improve tree growth or yield in an apple replant site

Apple replant disease (ARD) is a disease complex that reduces survival, growth and yield of replanted trees, and is often encountered in establishing new orchards on old sites. Methyl bromide (MB) has been the fumigant used most widely to control ARD, but alternatives to MB and cultural methods of control are needed. In this experiment, we evaluated the response of soil microbial communities and tree growth and yield to three pre-plant soil treatments (compost amendment, soil treatment with a broad-spectrum fumigant, and untreated controls), and use of five clonal rootstock genotypes (M.7, M.26, CG.6210, G.30 and G.16), in an apple replant site in Ithaca, New York. Polymerase chain reaction (PCR)—denaturing gradient gel electrophoresis (DGGE) analysis was used to assess changes in the community composition of bacteria and fungi in the bulk soil 8, 10, 18 and 22 months after trees were replanted. PCR-DGGE was also used to compare the community composition of bacteria, fungi and pseudomonads in untreated rhizosphere soil of the five rootstock genotypes 31 months after planting. Tree caliper and extension growth were measured annually in November from 2002 to 2004. Apple yield data were recorded in 2004, the first fruiting year after planting. Trees on CG.6210 rootstocks had the most growth and highest yield, while trees on M.26 rootstocks had the least growth and lowest yield. Tree growth and yield were not affected by pre-plant soil treatment except for lateral extension growth, which was longer in trees growing in compost-treated soil in 2003 as compared to those in the fumigation treatment. Bulk soil bacterial PCR-DGGE fingerprints differed strongly among the different soil treatments 1 year after their application, with the fingerprints derived from each pre-plant soil treatment clustering separately in a hierarchical cluster analysis. However, the differences in bacterial communities between the soil treatments diminished during the second year after planting. Soil fungal communities converged more rapidly than bacterial communities, with no discernable pattern related to pre-plant soil treatments 10 months after replanting. Changes in bulk soil bacterial and fungal communities in response to soil treatments had no obvious correlation with tree performance. On the other hand, rootstock genotypes modified their rhizosphere environments which differed significantly in their bacterial, pseudomonad, fungal and oomycete communities. Cluster analysis of PCR-DGGE fingerprints of fungal and pseudomonad rhizosphere community DNA revealed two distinct clusters. For both analyses, soil sampled from the rhizosphere of the two higher yielding rootstock genotypes clustered together, while the lower yielding rootstock genotypes also clustered together. These results suggest that the fungal and pseudomonad communities that have developed in the rhizosphere of the different rootstock genotypes may be one factor influencing tree growth and yield at this apple replant site.     

Reciprocal transfer effects on denitrifying community composition and activity at forest and meadow sites in the Cascade Mountains of Oregon

In order to examine the effects of disturbance, vegetation type, and microclimate on denitrification and denitrifier community composition, experimental plots were established at the H. J. Andrews Experimental Forest in the Cascade Mountains of Oregon. Soil cores were reciprocally transplanted between meadow and forest and samples were collected after 1 and 2 years. Denitrifying enzyme activity (DEA) was measured using the acetylene block assay and terminal restriction length polymorphism profiles were generated with nosZ primers that target the gene coding for nitrous oxide reductase. Nitrate concentrations, C mineralization, and water content were measured to gain additional insights into soil properties controlling DEA. Meadow soils were significantly higher in DEA than forest soils, and the highest DEA levels were observed in cores transferred from the meadow into the forest. Nitrate concentrations were also different between forest and meadow soils, but did not correlate to DEA. DEA was higher in open versus closed cores, suggesting an association between denitrification and the rhizosphere. Denitrifier communities of undisturbed forest and meadow soils shifted through a 4-year period but remained distinct from each other. Similarly, denitrifier communities clustered by vegetation type of origin regardless of manipulation, suggesting that the overall denitrifier communities are well buffered against environmental changes.     

Kinetic Parameters of Gross N Mineralization of Peat Soils as Related to the Composition of Soil Organic Matter

Peat land has been considered as an alternative type of land for agricultural development especially in the tropics. In the present study, the N-supplying capacity, one of the most important soil properties in terms of crop production, of peat soils was examined. Ten peat soil samples were collected from Indonesia, Malaysia, and Japan. Gross N mineralization in the soil samples was estimated using a zero-order model, and kinetic parameters of mineralization were determined using a simple type model. Soil organic matter composition was investigated using ¹³C CPMAS NMR. Mineralization potential ( N ₀), apparent activation energy ( E _a), and mineralization rate constant ( k ) ranged between 571–2,445 mg kg⁻¹, 281–8,181 J mol⁻¹, and 0.009–0.020 d⁻¹, respectively. Although none of the parameters showed a significant correlation with the soil C/N ratio, a negative correlation was observed between the k value and the ratio of the proportion of alkyl C in total C to that of O -alkyl C estimated by ¹³C CPMAS NMR. The latter suggested that the k values were higher in the peat soils relatively rich in readily decomposable organic matter including carbohydrates.     

福建早稻产量结构要素的气象影响研究

通过对福建早稻多年田间观测数据与气象资料的相关和回归分析,研究气象条件对早稻产量结构要素的影响,结果表明穗结实粒数是造成早稻产量年际变化的主要因素,幼穗分化到乳熟期的光温水条件对早稻产量起着主要作用。     

西安草滩渭河古河漫滩沉积与洪水变化

根据野外调查、历史文献记录和106个样品的粒度分析,对草滩渭河沉积剖面的洪水变化进行了研究。结果表明,渭河300年来洪水沉积分层明显,对洪水的发生和短期降水量变化反映清楚,分辨率高,能够作为很好地指示洪水和降水量变化的指标。CT剖面厚度约4.5 m,为古洪水沉积层,剖面随深度变化具有明显的粗细变化节律。共分为21个沉积层,指示了21次较大规模的洪水。CT剖面反映的21个阶段的洪水深度和规模由大到小的变化顺序为:第13阶段>第5阶段>第17阶段>第14阶段>第12阶段>第6阶段>第2阶段>第1阶段>第18阶段>第4阶段>第3阶段>第10阶段>第11阶段>第8阶段>第21阶段>第9阶段>第15阶段>第20阶段>第19阶段>第16阶段>第7阶段,其中第13,5,17,14,12,6,2,1阶段为特大洪水阶段,第18,4,3,10,11,8,21,9,15,20,19,16,7阶段为大洪水阶段。CT剖面粒度成分显著大于120年来的洪水沉积,反映了草滩剖面洪水发生时,水动力强,流量大,指示当时降水量应当较多。西安草滩CT剖面第1,2,5,6,12,13,14,17层沉积时,高出河床之上的洪水深度大于6.5 m,其余15个阶段的洪水深度等于或小于6.5 m。     

不同类型土壤胡敏素组成的研究

胡敏素(HM)是腐殖物质的主要组成部分,在碳截获、土壤结构、养分保持、生物地球化学循环等方面都占有重要的作用.采用Pallo修改法对HM进行了分组,将其分为铁结合胡敏素(HMi)、粘粒结合胡敏素(HMc)和不溶性胡敏素(HMr).并将这三种物质定义为HM的组成,同时把HMi/HMc和(HMi HMc)/HM作为HM组成的表征指标.研究了不同类型土壤的HM组成.结果表明:不同类型土壤中HM各组分含量.HMi/HMc,(HMi HMc)/HM,△lgk均各不相同;(HMi HMc)/HM>20%;除黑钙土外,HMi/HMc>1,且HM组成中HMr含量最多,HMi其次,HMc最少;HMi相对数量为黑土最高,黑钙土最低,HMc相对数量为黑钙土最高,棕壤最低,HMr相对数量为水稻土最高,黑土最低.在不同类型土壤(水稻土除外)中可溶性HM组分的△lgk值为HMi>HMc,HMi的分子结构比HMc的简单,而且棕壤HMi,HMc的△lgk值均最高,结构最简单.     

The future of tropical species in secondary forests: A quantitative review

Deforestation and degradation of tropical old-growth forests has the potential to cause catastrophic species extinctions. In this review, we assess whether regenerating secondary forests (SF) can support species typically found in old-growth forest (OG) and so prevent extinctions. We review 65 studies that compare faunal diversity in SF and corresponding OG, and compare the similarity of species composition both within and between these two forest types using the Sorensen, Morisita-Horn and Sorensen-Chao indices. Comparisons between traditional similarity indices and Sorensen-Chao, which minimizes sampling biases, indicated that limited sampling effort consistently reduced apparent similarity between SF and OG and that similarity between SF and OG is actually higher than previously appreciated. Similarity, which ranges from 0 to 1, varied from 0.49 to 0.92 between replicate OG sites and was correlated with similarity between SF and OG. This correlation might be an artefact of variation among studies in sampling effort, especially for vertebrates where small samples reduce apparent similarity across all comparisons, as well as a real effect of variation among studies in landscape heterogeneity and the presence of species with patchy distributions. Therefore, similarity between SF and OG cannot be interpreted without an understanding of background variation in OG. Similarity between different SF sites provided no evidence that disturbance specialists dominate SF. Similarity to OG increased rapidly with SF age; when SF was contiguous with OG; when SF was growing in small clearings; and after low intensity land uses including clearing only, shifting agriculture and tree plantations. This describes the most frequently observed tropical SF; isolated from roads and on hilly terrain unsuitable for mechanized agriculture. Thus, our analyses indicate that tropical SF can play an important role in biodiversity conservation particularly when OG forests are nearby. An important caveat remains, however. Abundance, geographic range and levels of habitat specialization are often related. Widespread, abundant, habitat generalists might dominate similarity analyses even when relatively rare OG specialists are present. Additional species-level analyses of habitat specialization will be needed before the conservation value of tropical SF is fully understood.     

不同年限稻鸭共作对水体藻类群落结构的影响

为探究不同规模、不同年限稻鸭共作系统水体藻类群落组成及多样性的差异,通过设置不同年限(4、20 a)和不同规模(0.067、0.200、0.333 hm~2)稻鸭共作田,利用高通量测序等手段,分析稻鸭共作田水体藻类多样性及群落结构的变化规律。结果表明:稻鸭共作田水体藻类的丰富度指数较非稻鸭共作田高,长期稻鸭共作田水体藻类Ace丰富度指数较短期共作田高,物种数增多;稻鸭共作田与非稻鸭共作田水体藻类优势种均为裸藻、绿藻、蓝藻,但稻鸭共作田绿藻、蓝藻的相对丰度高于非稻鸭共作田,另外稻鸭共作田规模大小影响蓝藻的相对丰度,规模越大蓝藻相对丰度越低;稻鸭共作田藻类多样性指数比非稻鸭共作田高,水体藻类群落结构差异较大,稻鸭共作系统的水体藻类群落结构表现出一定的相似性。冗余分析表明,对于稻鸭共作后期而言,影响非稻鸭共作田水体藻类群落结构的主要环境因子是溶解氧,而影响稻鸭共作水体藻类群落结构的环境因子是可溶性钾和pH。研究表明,长期稻鸭共作系统提高水体藻类多样性,改变藻类群落组成,从而影响农田水体生态环境。